This invention relates to a cryogenic fluid Dewar container. More particularly, the present invention relates to a Dewar container holding a volume of cryogenic fluid as a liquefied-gas and comprising a heat exchanger system that is useful for delivering an on-demand supply of breathable air, which has been vaporized from the cryogenic fluid, to a user working in an environment where the air is insufficient to support life. This occurs independent of the spatial orientation of the Dewar and the direction of the encountered gravitational field. At the same time that the heat exchanger system of the present invention is vaporizing the cryogenic fluid to form gas, it also holds the internal pressure at a level which provides adequate flow rates required for breathing.
For purpose of this disclosure, a cryogenic fluid may be regarded as a substance having a boiling temperature below .+-.150.degree. C.
The Dewar container of the present invention comprises an inner shell which is filled with a cryogenic fluid as a liquefied-gas and is vacuum sealed inside an outer shell. This provides an insulating space between the shells that helps prevent ambient heat transfer to the cryogenic fluid. The Dewar further comprises a plurality of heat exchangers that are connected in series. These heat exchangers are specifically constructed to first vaporize the cryogenic fluid to a gaseous state and then warm the gas to about ambient temperature. The gas, which is preferably a breathable air mixture, is then delivered to a pressure regulator which governs the airflow to an on-demand facepiece worn by the user to support the user's breathing. This air delivery is accomplished without the use of moving parts. A further advantage of the present container over high-pressure gas containers is that the gas is stored as a low (cryogenic) temperature fluid and at a relatively low pressure. Therefore the weight of the low-pressure, cryogenic fluid container is substantially less than the weight of a high pressure gas container holding a comparable volume of breathable air.